Chronic toxicity of 2-methyl-4-chlorophenoxyacetic acid (MCPA) in mice.

One of the phenoxy herbicides, 2-methyl-4-chlorophenoxyacetic acid (MCPA) was soaked with pellet dissolved by corn oil and given to ICR male mice for 18 months at levels of 40, 200, 1,000 and 5,000 ppm (about 3.9, 19.0, 95.6 and 566.4 mg/kg/day, respectively). The animals were then placed on a control diet for 12 months. Treatment with 5,000 ppm of MCPA resulted in a significantly decreased survival rate of the mice. Histopathological examination of mice treated with 40 ppm MCPA revealed the occurrence of leukemia which showed neoplastic infiltration in the liver. No adverse effect of the gallbladder, except for papillary proliferation, was noted at all the dose levels of the experimental groups.